I've used Eagletree loggers. Chiefly for current draw and measuring RPM. The ability to measure these aspects with the vehicle whilst under way is an absolute boon of modern microprocessor technology.

I do have a plug-in GPS module, which can measure speed, but haven't used that part on a sub, only in aeroplanes, cars and boats. Sadly the signal won't penetrate through water, which would mean surface running on, or fixing it on a separate pontoon.

You can always measure speed the old fashioned way with a stop watch timing over a measured section of pond/lake/pool. Accurate enough for me.

Thanks Subculture!Eagletree uses a pitot tube system for speed for both airplanes and boats and the output from their sensor is in actual MPH as in your car. The lowest speed is 9 MPH and top speed is 350 MPH way too fast for our subs. Their pressure sensor is a 0-2 psi sensor. My guess is our subs may max out at maybe 15 MPH? Just thought maybe someone had actually measured the speed either on the surface or underwater?

Thanks!Have you used the pressure sensor on your sub? The reason I ask is that the eagletree pressure system will only start reading at 9MPH! If our subs max out at 7 MPH then it would seem you cannot get any reading? Maybe next time you are doing a test you could use your GPS? The way I am looking at this is if a 0-2 psi sensor shows 350 MPH at 2 psi full scale then at 1 psi it would be maybe half that speed? So:PSI MPH1.00 = 175.000.50 = 87.500.30 = 26.250.15 = 3.940.07 = 0.280.03 = 0.01Just trying to use a correct pressure sensor.